Preprints
https://doi.org/10.5194/acp-2021-270
https://doi.org/10.5194/acp-2021-270

  20 Apr 2021

20 Apr 2021

Review status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

An organic crystalline state in ageing atmospheric aerosol proxies: spatially resolved structural changes in levitated fatty acid particles

Adam Milsom1, Adam M. Squires2, Jacob A. Boswell2, Nicholas J. Terrill3, Andrew D. Ward4, and Christian Pfrang1,5 Adam Milsom et al.
  • 1University of Birmingham, School of Geography, Earth and Environmental Sciences, Edgbaston, B15 2TT, Birmingham, UK
  • 2University of Bath, Department of Chemistry, South Building, Soldier Down Ln, Claverton Down, BA2 7AX, Bath, UK
  • 3Diamond Light Source, Diamond House, Harwell Science and Innovation Campus, OX11 0DE, Didcot, UK
  • 4Central Laser Facility, Rutherford Appleton Laboratory, Harwell Campus, OX11 0QX, Didcot, UK
  • 5Department of Meteorology, University of Reading, Whiteknights, Earley Gate, RG6 6BB, Reading, UK

Abstract. Organic aerosols are key components of the Earth’s atmospheric system. The phase state of organic aerosols is known to be a significant factor in determining aerosol reactivity, water uptake and atmospheric lifetime – with wide implications for cloud formation, climate, air quality and human health. Unsaturated fatty acids contribute to urban cooking emissions and sea spray aerosols. These compounds, exemplified by oleic acid and its sodium salt, are surface active and have been shown to self-assemble into a variety of liquid-crystalline phases upon addition of water. Here we observe a crystalline acid–soap complex in acoustically levitated oleic acid–sodium oleate particles. We developed a synchrotron-based simultaneous Small-Angle & Wide-Angle X-ray Scattering (SAXS/WAXS)/Raman microscopy system to probe physical and chemical changes in the proxy during exposure to humidity and the atmospheric oxidant ozone. We present a spatially resolved structural picture of a levitated particle during humidification, revealing a phase gradient consisting of a disordered liquid crystalline shell and crystalline core. Ozonolysis is significantly slower in the crystalline phase compared with the liquid phase and a significant portion (34 ± 8 %) of unreacted material remains after extensive oxidation. We present experimental evidence of inert surface layer formation during ozonolysis, taking advantage of spatially resolved simultaneous SAXS/WAXS experiments. These observations suggest atmospheric lifetimes of surface-active organic species in aerosols are highly phase dependent, potentially impacting on climate, urban air quality and long-range transport of pollutants such as Polycyclic Aromatic Hydrocarbons (PAHs).

Adam Milsom et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-270', Anonymous Referee #1, 22 May 2021
  • RC2: 'Comment on acp-2021-270', Anonymous Referee #2, 23 May 2021
    • AC1: 'Reply on RC2 - supplement access issue', Christian Pfrang, 23 May 2021

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-270', Anonymous Referee #1, 22 May 2021
  • RC2: 'Comment on acp-2021-270', Anonymous Referee #2, 23 May 2021
    • AC1: 'Reply on RC2 - supplement access issue', Christian Pfrang, 23 May 2021

Adam Milsom et al.

Adam Milsom et al.

Viewed

Total article views: 431 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
311 102 18 431 28 3 8
  • HTML: 311
  • PDF: 102
  • XML: 18
  • Total: 431
  • Supplement: 28
  • BibTeX: 3
  • EndNote: 8
Views and downloads (calculated since 20 Apr 2021)
Cumulative views and downloads (calculated since 20 Apr 2021)

Viewed (geographical distribution)

Total article views: 427 (including HTML, PDF, and XML) Thereof 427 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 19 Sep 2021
Download
Short summary
Atmospheric aerosols can be solid, semi-solid or liquid. This phase state can impact key aerosol processes such as oxidation and water uptake, affecting cloud droplet formation and urban air pollution. We have observed a solid crystalline organic phase in a levitated proxy for a cooking emissions, oleic acid. Spatially resolved structural changes were followed during ageing by X-ray scattering, revealing phase gradients, aggregate products and a markedly reduced ozonolysis reaction rate.
Altmetrics